SRP54_N

SRP54-type protein, helical bundle domain

SMART accession number:

SM00963

Description:

This entry represents the N-terminal helical bundle domain of the 54 kDa SRP54 component, a GTP-binding protein that interacts with the signal sequence when it emerges from the ribosome. SRP54 of the signal recognition particle has a three-domain structure: an N-terminal helical bundle domain, a GTPase domain, and the M-domain that binds the 7s RNA and also binds the signal sequence. The extreme C-terminal region is glycine-rich and lower in complexity and poorly conserved between species.

This entry represents the N-terminal helical bundle domain of the 54 kDa SRP54 component, a GTP-binding protein that interacts with the signal sequence when it emerges from the ribosome. SRP54 of the signal recognition particle has a three-domain structure: an N-terminal helical bundle domain, a GTPase domain, and the M-domain that binds the 7s RNA and also binds the signal sequence. The extreme C-terminal region is glycine-rich and lower in complexity and poorly conserved between species.

Other proteins with this domain include signal recognition particle receptor alpha subunit (docking protein), an integral membrane GTP-binding protein which ensures (in conjunction with SRP) the correct targeting of nascent secretory proteins to the endoplasmic reticulum membrane; and bacterial FtsY protein, which is believed to play a similar role to that played by the eukaryotic docking protein.

Crystal structure of the NG domain from the signal-recognition particlereceptor FtsY.

Nature. 1997; 385: 365-8

Display abstract

Newly synthesized proteins destined either for secretion or incorporationinto membranes are targeted to the membrane translocation machinery by aubiquitous system consisting of a signal-recognition particle (SRP) andits receptor. Both the SRP receptor and the protein within the SRP thatbinds the signal sequence contain GTPases. These two proteins, togetherwith the RNA component of the SRP, form a complex and thereby regulateeach other's GTPase activity. Here we report the structure of theGTPase-containing portion of FtsY, the functional homologue of the SRPreceptor of Escherichia coli, at 2.2 A resolution without boundnucleotide. This so-called NG domain displays similarities to theRas-related GTPases, as well as features unique to the SRP-type GTPases,such as a separate amino-terminal domain, an insertion within the p21ras(Ras) effector domain, and a wide-open GTP-binding region. The structureexplains the low affinity of FtsY for GTP, and suggests rearrangementsthat may occur on nucleotide binding. It also identifies regionspotentially involved in the transmission of signals between domains and ininteractions with regulatory proteins.